Power and control cable installations typically require some form of protection from environmental agents and hazards. For instance, power and control cables installed in nuclear generating plants or petrochemical facilities require protection from fire and explosion hazards. The protection is required to ensure that cables remain intact after an explosion or during a fire event, so that the processes and systems can remain operational, and/or be shut down in a controlled manner.
The U.S. Nuclear Regulatory Commission (NRC), for example, requires additional protection safeguard, such as redundant trains or cable trays for Class 1E power and control systems. For instance, NRC Regulations 10 CFR 50, Appendix R, mandate that “One train of equipment necessary to achieve hot shutdown from either the control room or emergency control station(s) must be maintained free of fire damage by a single fire, including an exposure fire” for a ‘hot’ or operational shutdown of a facility. It will be appreciated that as the required redundant trains for a hot shutdown are often located within a common fire area in close proximity to each other, e.g. with less than 20 foot separation, the redundant trains must be separated by a barrier having a 3-hour fire rating to ensure that one of the redundant trains remains free of fire damage and operational. According to the NRC, if the fire area with the redundant trains is protected with an automatic fire suppression system, then the 3-hour fire rating can be reduced to a 1-hour fire rating.
In oil refineries and chemical plants, an explosion is typically the precursor to and one of the major causes of fires. The construction of the enclosure systems protecting the cable trays need to be robust to ensure the fire resistance of the enclosure is not compromised as a result of blast pressure or debris impact arising from an explosion or flash fire in the plant. Maintaining the integrity and operability of the cables after an explosion or fire allows plant or emergency personnel to perform an orderly shutdown of the affected systems, for instance, from the safety of a fire-rated or protected control room, which may also include equipment for monitoring and controlling other plant processes and equipment. It will be appreciated that the ability to continue to monitor and shut down other systems or processes in the vicinity, which could lead to further failures or explosions, provides emergency personnel (e.g. fire fighters) with the opportunity to extinguish the fire and minimize further plant damage.
In view of the importance of providing protective enclosures for cables and the like, there remains a need for improvements in the art.